Scanning type image viewing optical system

ABSTRACT

A scanning-type image viewing optical system has a light source for emitting luminous flux; a main scanning means for scanning luminous flux in a first direction; a sub-scanning means for scanning luminous flux in a second direction different from the first direction; and an eyepiece lens for directing luminous flux scanned by the two scanning means to the pupil of an observer, wherein the main scanning means has a conjugate relationship with the pupil position of the observer via the eyepiece lens, and when the pupil diameter, i.e., the luminous flux diameter of the incident luminous flux at the pupil position of the observer, is designated d and the main scan diameter, i.e., the luminous flux diameter exiting the main scanning means, is designated d&#39;, the conjugate magnification β calculated by d/d&#39; satisfies the conditional equation 1.2≦β.

CROSS-REFERENCE OF RELATED APPLICATIONS

This application is based on Application No. 10-143848 filed in Japan,the content of which is hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a scanning-type image viewing opticalsystem. and specifically relates to a scanning type image viewingoptical system which provides an image to an observer by scanningluminous flux emitted from a light source on the pupil of the observerusing the after image of the observer, this system being for use in, forexample, head-up displays and head-mounted displays.

DESCRIPTION OF THE RELATED ART

FIG. 3 is a structural diagram of a conventional scanning-type imageviewing optical system. In FIG. 3, the luminous flux emitted from alight source 1 is modulated to a light intensity by a modulator 2, andimpinges a first scanning mirror 3. The first scanning mirror 3 issupported by a center rotating shaft 3a so as to be rotatable, androtates at a predetermined amplitude and frequency. The incidentluminous flux is reflected and simultaneously scans in a first scandirection via this mirror rotation.

The luminous flux scanned by the first scanning mirror 3 impinges asecond scanning mirror 4. The second scanning mirror 4 has a rotatingshaft 4a perpendicular to the rotating shaft 3a of the first scanningmirror 3, and rotates at a predetermined amplitude and frequency. Theincident luminous flux is reflected and simultaneously scans in a secondscan direction via this mirror rotation. In this optical system, thefirst scanning direction and the second scanning direction are mutuallyperpendicular.

The luminous flux scanned via the first and second scanning mirrors 3and 4 is reflected by a semitransparent surface 5, and enters theeyepiece 6. One surface of the eyepiece 6 is a reflective surface 6a,which bends the luminous flux again to the semitransparent surface 5side. The bent luminous flux passes through the semitransparent surface5, and impinges the pupil 7 of an observer. A projection image isobserved by the observer via the after image. Since this image viewingoptical system does not use a two-dimensional display element such as aliquid crystal display element, it can provide a highly detailedprojection image without being affected by the several number of pixelsof the display element.

The scanning determined by the scanning mirrors 3 and 4 when displayinga specific projection image via the image viewing optical system of theaforesaid construction is described below with reference to FIG. 4.Hypothetically consider displaying an image of high-vision equivalence.The aspect ratio of a high-vision image is 16:9, the number of framesthat must be displayed per second is 60 frames, and approximately 1,000horizontal scan lines are required.

The scanning frequency in the horizontal direction is 60 kHz determinedby the number of horizontal scan lines multiplied by the number offrames, and the number of vertical scan lines is 60 Hz determined by thenumber of frames. In this way, the required scanning frequency isrelatively greater in the horizontal direction compared to the verticaldirection, and the required scanning angle is also greater in thehorizontal direction, such that scanning in the horizontal directionmust be overwhelmingly fast. In general, scanning in the horizontaldirection is termed the main scan, and scanning in the verticaldirection is termed the sub-scan.

Since the second scanning mirror 4 is optically disposed behind thefirst scanning mirror 3 in the optical system of the conventional artshown in FIG. 3, the second scanning mirror 4 must be constructed largerthan the first scanning mirror 3 since the scanning angle must besufficiently large to cover the first scanning mirror 3. Accordingly,the first scanning mirror 3 used for the main scan is generally as smallas possible.

In a conventional image viewing optical system, in order for the firstscanning mirror 3, which performs the main scan, to be constructed assmall as possible, the system is constructed so that the mirror 3 isdisposed at a conjugate position to the pupil 7.

FIG. 2(a) briefly shows the relationships among the pupil d0, angle offield a0, main scan diameter d'0, and scan angle a'0 when the conjugatemagnification β calculated by the pupil diameter/main scan diameter is 1(equal magnification) in an optical system in which the main scanningmember is arranged at a position having a conjugate relationship to thepupil. The angle of field and the scan angle are the incidence angle ofthe extra off-axial rays 12 at the pupil 7 position and the exit angleof the extra off-axial rays 12 at the main scanning member 3 position,respectively. The pupil diameter and the main scan diameter are theluminous flux diameters at the pupil 7 position and at the main scanningmember 3 position. respectively. The viewable projection image rangeincreases as the angle of field becomes larger, and the viewable pupilposition range increases as the pupil diameter becomes larger.

FIG. 2(a) schematically shows the layout of a conventional opticalsystem. In FIG. 2(a), the conjugate magnification β is 1, such thatd0=d'0. At the same time, a0=a'0. In a conventional optical system withspecific pupil diameter and angle of field. the main scanning member isconstructed so as to rotate with a large number of oscillations, whichmakes it difficult to increase the scanning speed for high resolutiondisplay, such that the values of both the main scan diameter and thescan angle are averaged to reduce the main scan diameter and the scanangle.

Furthermore, in a conventional image viewing optical system, the mainscan diameter is increased to obtain an adequate pupil diameter, therebymaking it difficult to increase the scanning speed for high resolutiondisplay. In conventional optical systems, it is also difficult to assurea pupil diameter which can cope with eye movement.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an improvedscanning-type image viewing optical system.

A further object of the present invention is to provide a scanning-typeimage viewing optical system capable of enlargement of the pupildiameter without enlarging the main scanning member.

These objects are attained by a scanning-type image viewing opticalsystem comprising:

a light source for emitting luminous flux; a main scanning means forscanning luminous flux in a first direction; a sub-scanning means forscanning luminous flux in a second direction different from the firstdirection; and an eyepiece lens for directing luminous flux scanned bythe two scanning means to the pupil of an observer, wherein the mainscanning means has a conjugate relationship with the pupil position ofthe observer via the eyepiece lens, and when the pupil diameter, i.e.,the luminous flux diameter of the incident luminous flux at the pupilposition of the observer, is designated d and the main scan diameter.i.e., the luminous flux diameter exiting the main scanning means, isdesignated d', the conjugate magnification β calculated by d/d'satisfies the conditional equation 1.2≦β.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and features of this invention will become clearfrom the following description, taken in conjunction with the preferredembodiments with reference to the accompanying drawings, in which:

FIG. 1(a) is a layout diagram showing the arrangement of the structuralelements of the optical system of the present invention on a linearoptical axis;

FIG. 1(b) shows the positional relationship in the construction of FIG.1(a);

FIG. 2(a) shows the relationships among the pupil diameter, angle ofview, main scan diameter, and scan angle in a conventional opticalsystem;

FIGS. 2(b) and 2(c) show the relationships among the pupil diameter,angle of view, main scan diameter, and scan angle in an embodiment ofthe present invention;

FIG. 3 is a structural view of a scanning-type image viewing opticalsystem common to both the conventional art and the present invention;and

FIG. 4 illustrates the display of a high-vision equivalent image.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A perspective view showing the general construction of the scanning-typeimage viewing optical system of the present embodiment common also tothe conventional scanning-type image viewing optical system is shown inFIG. 3. FIG. 1(a) is a layout diagram briefly showing the structuralelements of the scanning-type image viewing optical system of FIG. 3viewed on line 13 which represents the optical axis in FIG. 3.

The luminous flux emitted from the light source 1 is scanned by the mainscanning mirror 3 and the sub-scanning mirror 4, and subsequently form ascan image at the scan image forming position. The luminous flux formingthe scan image arrives at the pupil 7 of an observer via the eyepiecelens 6, and forms a retinal image on the retina 9 of the eyeball 8. Theobserver views a virtual image at the virtual image position 11 via theretinal image. FIG. 1(b) illustrates the relationships among the retinalimage 9a, the scan image 10a, the virtual image 11a, the eyepiece lens6, and the pupil lens 7.

FIG. 1 does not show the strict layout positions of each structuralelement, but rather shows the optically approximate relationships amongthe structural elements. In the present embodiment, the main scanningmirror 3 is disposed at a position which is the approximate conjugateposition with the pupil 7 through the eyepiece lens 6, and theconstruction is such that the conjugate magnification p satisfies theconditional equation 1.2≦β≦7 in contrast to the conventional example ofβ=1 shown in FIG. 2(a). By satisfying this condition, the main scanningmirror 3 can be rendered more compact, and the pupil diameter can beenlarged compared to a conventional scanning-type image viewing opticalsystem.

In correspondence to the conventional art shown in FIG. 2(a), FIGS. 2(b)and 2(c) show the relationships among the pupil diameters d1 and d2,angles of field al and a2, main scan diameters d'1 and d'2, and scanangles a'1 and a'2 of the scanning-type image viewing optical system ofthe present embodiment. To facilitate comparison, the angle of field inFIG. (2a), (b), and (c) are identical, i.e., a0=a1=a2.

As shown in FIG. 2(b), when the pupil diameter d1 equals the pupildiameter d0, the main scan diameter d1 is smaller than the main scandiameter d'0 of FIG 2(a). that is, the main scanning mirror 3 can berendered more compact. When the main scan diameter d'2 equals the mainscan diameter d'0 of FIG. 2(a) as shown in FIG. 2(c), the pupil diameterd2 is larger than the pupil diameter d0 of FIG. 2(a). That is, the pupildiameter can be enlarged. In FIG. 2(b) and (c), the scan angles a'1 anda'2 are greater than the scan angle a'0 of FIG. 2(a).

Table 1 shows examples of specific numeric values for the conjugatemagnification, the main scan diameter, the pupil diameter, the scanangle, and the angle of field of the present embodiment. Specificnumeric examples for the conventional art (corresponds to FIG. 2(a)) areshown for the purpose of comparison. Examples 1, 2, and 3 use threedifferent values for the pupil diameter and the main scan diameter andare given as numeric examples of the conventional art. Examples 4, 5,and 6 use the same numeric values for the pupil diameters as in theconventional examples 1, 2, and 3, but use difference values for theconjugate magnification (corresponds to FIG. 2(b)). Examples 1, 2, 3 andExamples 7, 8, and 9 use the same numeric values for the main scandiameter as in the conventional examples 1, 2, and 3, but use differentvalues for the conjugate magnification (corresponds to FIG. 2(c)).

                  TABLE 1                                                         ______________________________________                                        Conjugate     Main Scan                                                                              Pupil    Scan  Angle of                                Magnification Diameter Diameter Angle Field                                   ______________________________________                                        Conven-                                                                              1.00       1.00     1.00   10.00 10.00                                 tional                                                                        Example 1                                                                     Conven-                                                                              1.00       5.00     5.00   7.00  7.00                                  tional                                                                        Example 2                                                                     Conven-                                                                              1.00       10.00    10.00  5.00  5.00                                  tional                                                                        Example 3                                                                     Example 1                                                                            1.25       1.00     1.25   12.43 10.00                                 Example 2                                                                            1.25       5.00     6.25   8.73  7.00                                  Example 3                                                                            1.25       10.00    12.50  6.24  5.00                                  Example 4                                                                            1.25       0.80     1.00   12.43 10.00                                 Example 5                                                                            1.25       4.00     5.00   8.73  7.00                                  Example 6                                                                            1.25       8.00     10.00  6.24  5.00                                  Example 7                                                                            2.00       1.00     2.00   19.43 10.00                                 Example 8                                                                            2.00       5.00     10.00  13.80 7.00                                  Example 9                                                                            2.00       10.00    20.00  9.93  5.00                                  ______________________________________                                    

As can be understood from Table 1. when the value of the pupil diameteris the same as in the conventional examples (i.e. examples 4, 5, 6), themain scan diameter can be smaller. Furthermore, when the value of themain scan diameter is the same as in the conventional example (i.e.,examples 1, 2, 3 and examples 7, 8, 9), the pupil diameter can belarger. This effect becomes more pronounced as the conjugatemagnification increases. When the conjugate magnification is excessivelylarge, a desirable scan angle cannot be obtained, i.e., a desirableangle of field cannot be obtained.

As stated above, the scanning-type image viewing optical system of thepresent embodiment provides a construction which allows the mainscanning member to be rendered smaller, by reducing the main scandiameter. In this way it is possible to oscillate the main scan memberat high speed, and display an image of higher resolution. Furthermore,the pupil diameter can be enlarged without increasing the main scandiameter. That is, the pupil diameter can be enlarged without decreasingthe scanning speed.

Although the present invention has been fully described by way ofexamples with reference to the accompanying drawings, it is to be notedthat various changes and modification will be apparent to those skilledin the art. Therefore, unless otherwise such changes and modificationsdepart from the scope of the present invention, they should be construedas being included therein.

What is claimed is:
 1. A scanning-type image viewing optical systemcomprising:a light source for emitting luminous flux; a main scanningmeans for scanning the luminous flux in a first direction; asub-scanning means for scanning the luminous flux in a second directiondifferent from the first direction; and an eyepiece lens for directingthe luminous flux scanned by the two scanning means to a pupil of anobserver, wherein the main scanning means has a conjugate relationshipwith the pupil of the observer via the eyepiece lens, and wherein thefollowing condition is fulfilled:

    1.2≦β

where β represents a conjugate magnification calculated by d/d', whereina pupil diameter is designated d and a main scan diameter is designatedd'.
 2. A scanning-type image viewing optical system as claimed in claim1, wherein the following condition is fulfilled:

    β≦7.


3. A scanning-type image viewing optical system as claimed in claim 1,wherein the first direction is perpendicular to the second direction. 4.A scanning-type image viewing optical system as claimed in claim 1,wherein the scanning-type image viewing optical system includes amodulator for modulating the luminous flux emitting from the lightsource.
 5. A scanning-type image viewing optical system as claimed inclaim 1, wherein the scanning-type image viewing optical system includesa semitransparent surface for reflecting the thus scanned luminous fluxfor transmission to the pupil of the observer.
 6. A scanning-type imageviewing optical device comprising:a light source for emitting luminousflux; a modulator for modulating the luminous flux as to form an image;a main scanning mirror for scanning the luminous flux in a main scanningdirection; a sub-scanning mirror for scanning the luminous flux in asub-scanning direction perpendicular to the main scanning direction; asemitransparent surface for reflecting the scanning luminous flux totransmit to a pupil of an observer; and an eyepiece lens for directingthe luminous flux scanned by the two scanning means to the pupil of theobserver, wherein the main scanning means has a conjugate relationshipwith the pupil of the observer via the eyepiece lens, and wherein thefollowing condition is fulfilled:

    1.2≦β

where β represents a conjugate magnification calculated by d/d', whereina pupil diameter is designated d and a main scan diameter is designatedd'.